Conventional computer systems provide the ability to operate peripheral content acquisition devices such as scanners or digital camera devices or such devices that can capture or acquire digital content or data such as a scanned document or digital photograph from a physical source. Once acquired, a computer system can visually render this content for a user or can transmit the content to remote recipients. In the operation of such conventional equipment and software, the user controls the computer system to instruct the connected content acquisition device to acquire data from a physical source, and software such as a device driver that communicates with the peripheral device (e.g., the scanner or camera device) is capable of receiving digital content from the device and storing it within a file in the computer system. The user of the computer system can then use a variety of different software applications to access the file containing the content acquired from the content acquisition device for many different purposes.
In some instances, a user of conventional systems such as those explained above may desire the ability to secure or “certify” the digital content within the file. This may include applying, for example, a digital signature or hash algorithm to the content of the file so that if the user, for example, transfers the file to a remote recipient, the remote recipient can access the digital signature associated with the file to determine whether the digital content within the file is authentic (i.e., is the content in the file upon which the digital signature was calculated). This conventional content authentication or certification verification process typically operates by computing a signature value on the content contained within the file and comparing that signature to the signature received along with the file. If the two signatures are the same, then the content is certified and the recipient can be sure the content has not been modified since the time the signature received with the content was generated on the content.
Several conventional software applications provide the ability to access a file of digital content stored within the computer system, such as a file in a file system containing scanned content, and to produce a signature or other certification on the digital content of the file. Once the signature is produced, the software application then associates that signature with the original file in order to create certified content in either a new file or in a file that replaces the original file. One example of a conventional application that provides this capability is Adobe Acrobat manufactured by Adobe Systems, Inc. of San Jose, Calif., U.S.A. Conventional versions of Adobe Acrobat allow a user to access a file of content stored on disk to produce a portable document format (PDF) version of that content that is certified with user supplied certification data.
By way of example, in order to certify scanned content received by the computer system from a scanner device coupled to the computer system, a user of a conventional computer system would operate scanner software in order to scan the original document content from the scanner device into a file located within a file system accessible to the computer system. The user can then operate the scanner software to print the acquired content, that is now stored within the file in a scanner data format, such as a raster image, on the disk in the computer system into another file stored in PDF format. The user is able to instruct the Adobe Acrobat software application to produce a certified version of the PDF file from the uncertified version of the raster image file. To do so, the user manually provides some certification data, such as an identity of the user or the computer system or the scanner device that acquired the file and based on this input from the user, Adobe Acrobat produces a certified copy of the content within a PDF file. User input may not be required, in which case Acrobat applied a standard signature algorithm to the raster data in the file obtain from the file system.
Thereafter, if the same or a different user (maybe on a different computer system) opens the certified PDF file using Adobe Acrobat, Acrobat will automatically recognize the file as containing certified content and will perform a certification function that checks the signature to determine if any modifications have been made to the certified content within the PDF file since the time the original certification was performed. If such modifications exist, the user attempting to open the content will be notified that the certification process failed and that the content that they are attempting to open and view may have been modified from its form that existed in the file just prior to the certification process.